Reprints are quite easy to spot.
Firstly, the front cover: Original books show a black mark on John’s neck, which was an inking error by the printer. Early reprints do not have this mark as the original photo was used to reproduce the cover. Subsequent reprints copied the cover photo from an original book, so the mark reappears.
The foolproof way to tell is from the cropping of the back cover photo. Look at the trees, top left, cropped on the two reprints here.